.flex() {
  display: flex;
}

.flex-row-center() {
  display: flex;
  align-items: center;
}

.flex-col-center() {
  .flex-row-center();
  flex-direction: column;
}

// 水平方向 水平垂直居中
.flex-center {
  .flex-row-center();
  justify-content: center;
}

.flex-between() {
  .flex-row-center();
  justify-content: space-between;
}
